What is the most obvious sign of puberty in girls? an increase in weight breast development the onset of menarche an increase in height?

The right option is; The onset of menarche

The onset of menarche is the same as the onset of menstruation which means the beginning of the menstrual period. Puberty is the period in life in which a boy or girl is capable of sexual reproduction. Puberty causes physical changes and affects boys and girls in a different way. This changes commonly happens between ages 12 and 16 for boys and ages 10 and 14 for girls. Signs of puberty in girls include breast development, hair growth in the pubic area and armpits and menstruation. Signs of puberty in boys include muscle growth, development of facial hair and deep voice, hair growth in the pubic area and armpits etc.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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maybe because its impossible for balloons to lift a whole entire house.